Fast forward for the initial state. The tutorial should start from there.

Author: antonarhipov

build.gradle.kts

@@ -1,7 +1,7 @@
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
-	id("org.springframework.boot") version "2.4.0-SNAPSHOT"
+	id("org.springframework.boot") version "2.4.0"
 	id("io.spring.dependency-management") version "1.0.10.RELEASE"
 	kotlin("jvm") version "1.4.10"
 	kotlin("plugin.spring") version "1.4.10"
@@ -15,7 +15,6 @@ repositories {
 	mavenCentral()
 	jcenter()
 	maven { url = uri("https://repo.spring.io/milestone") }
-	maven { url = uri("https://repo.spring.io/snapshot") }
 }
 
 dependencies {

settings.gradle.kts

@@ -1,15 +1 @@
-pluginManagement {
-    repositories {
-        maven { url = uri("https://repo.spring.io/milestone") }
-        maven { url = uri("https://repo.spring.io/snapshot") }
-        gradlePluginPortal()
-    }
-    resolutionStrategy {
-        eachPlugin {
-            if (requested.id.id == "org.springframework.boot") {
-                useModule("org.springframework.boot:spring-boot-gradle-plugin:${requested.version}")
-            }
-        }
-    }
-}
 rootProject.name = "chat-kotlin"

src/main/kotlin/com/example/kotlin/chat/controller/HtmlController.kt

@@ -0,0 +1,22 @@
+package com.example.kotlin.chat.controller
+
+import com.example.kotlin.chat.service.MessageService
+import com.example.kotlin.chat.service.vm.MessageVM
+import org.springframework.stereotype.Controller
+import org.springframework.ui.Model
+import org.springframework.ui.set
+import org.springframework.web.bind.annotation.GetMapping
+
+@Controller
+class HtmlController(val messageService: MessageService) {
+
+    @GetMapping("/")
+    fun index(model: Model): String {
+        val messages: List<MessageVM> = messageService.latest()
+
+        model["messages"] = messages
+        model["lastMessageId"] = messages.lastOrNull()?.id ?: ""
+
+        return "chat"
+    }
+}

src/main/kotlin/com/example/kotlin/chat/controller/MessageResource.kt

@@ -0,0 +1,37 @@
+package com.example.kotlin.chat.controller
+
+import com.example.kotlin.chat.service.MessageService
+import com.example.kotlin.chat.service.vm.MessageVM
+import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.*
+
+@RestController
+@RequestMapping("/api/v1/messages")
+class MessageResource(val messageService: MessageService) {
+
+    @GetMapping
+    fun latest(@RequestParam(value = "lastMessageId", defaultValue = "") lastMessageId: String): ResponseEntity<List<MessageVM>> {
+        val messages = if (lastMessageId.isNotEmpty()) {
+            messageService.after(lastMessageId)
+        } else {
+            messageService.latest()
+        }
+
+        return if (messages.isEmpty()) {
+            with(ResponseEntity.noContent()) {
+                header("lastMessageId", lastMessageId)
+                build<List<MessageVM>>()
+            }
+        } else {
+            with(ResponseEntity.ok()) {
+                header("lastMessageId", messages.last().id)
+                body(messages)
+            }
+        }
+    }
+
+    @PostMapping
+    fun post(@RequestBody message: MessageVM) {
+        messageService.post(message)
+    }
+}

src/main/kotlin/com/example/kotlin/chat/service/impl/FakeMessageService.kt

@@ -0,0 +1,44 @@
+package com.example.kotlin.chat.service.impl
+
+import com.example.kotlin.chat.service.MessageService
+import com.example.kotlin.chat.service.vm.MessageVM
+import com.example.kotlin.chat.service.vm.UserVM
+import com.github.javafaker.Faker
+import org.springframework.stereotype.Service
+import java.net.URL
+import java.time.Instant
+import kotlin.random.Random
+
+@Service
+class FakeMessageService : MessageService {
+
+    val users: Map<String, UserVM> = mapOf(
+        "Shakespeare"  to UserVM("Shakespeare", URL("https://blog.12min.com/wp-content/uploads/2018/05/27d-William-Shakespeare.jpg")),
+        "RickAndMorty" to UserVM("RickAndMorty", URL("http://thecircular.org/wp-content/uploads/2015/04/rick-and-morty-fb-pic1.jpg")),
+        "Yoda"         to UserVM("Yoda", URL("https://news.toyark.com/wp-content/uploads/sites/4/2019/03/SH-Figuarts-Yoda-001.jpg"))
+    )
+
+    val usersQuotes: Map<String, () -> String> = mapOf(
+        "Shakespeare"  to { Faker.instance().shakespeare().asYouLikeItQuote() },
+        "RickAndMorty" to { Faker.instance().rickAndMorty().quote() },
+        "Yoda"         to { Faker.instance().yoda().quote() }
+    )
+
+    override fun latest(): List<MessageVM> {
+        val count = Random.nextInt(1, 15)
+        return (0..count).map {
+            val user = users.values.random()
+            val userQuote = usersQuotes.getValue(user.name).invoke()
+
+            MessageVM(userQuote, user, Instant.now(), Random.nextBytes(10).toString())
+        }.toList()
+    }
+
+    override fun after(messageId: String): List<MessageVM> {
+        return latest()
+    }
+
+    override fun post(message: MessageVM) {
+        TODO("Not yet implemented")
+    }
+}